In a major milestone for the new HS2 line, the fourth and final machine being used to build the giant Northolt Tunnel beneath London has now been launched.
The 8.4-mile tunnel will connect Victoria Road in Ealing and West Ruislip in Hillingdon, carrying trains in and out of the capital.
The latest machine, named Lady Anne Byron, is the fourth tunnel boring machine (TBM) to be used to construct the Northolt Tunnel, and will bore 3.4 miles from Victoria Road to Greenpark Way in Greenford, alongside TBM Emily which launched in February.
The remaining five miles of twin-bored tunnels have been under construction since 2022. TBMs Sushila and Caroline have so far completed 2.5 miles of their dig.
All four TBMs are expected to complete their journeys in 2025, when they will be extracted from the ground at Greenpark Way.
Malcolm Codling, HS2’s Project Client Director for the London Tunnels, said: “HS2 has reached peak tunnelling activity as we focus on delivering the HS2 route between London and Birmingham.
“The launch of Anne is the culmination of many years of work for the London Tunnels team and a further triumph in British engineering.”
HS2’s London tunnels contractor, Skanska Costain STRABAG joint venture (SCS JV), has delivered a programme of work allowing for the TBM to launch at the Victoria Road Crossover Box, excavating the caterpillar-shaped box where trains will cross tracks on their way in and out of Old Oak Common station.
James Richardson, Managing Director for SCS JV, said: “The launch of TBM Anne is a milestone moment in this year of peak activity for the HS2 London Tunnels project.
“With a quartet of TBMs and over 20 construction sites all making significant progress, we are on course to deliver the high-speed line into central London, creating economic growth and opportunities at every step of the way.”
Anne is the eighth TBM launched across the HS2 project between London and the West Midlands. Almost half of the required 65 miles of twin-bored tunnels have now been excavated.
The machine was manufactured in Germany by Herrenknecht as one of ten purpose-built machines for HS2. Herrenknecht worked in collaboration with SCS JV to develop a cutting edge design to maximise productivity.
“Annie” is 170 metres long, weighing 1700 tonnes. Her cutterhead has a diameter of 9.11 metres.
She was lowered in parts into the 25 metre-deep crossover box at the end of 2023, where she was then assembled and prepared to begin her dig.
The TBM is an earth pressure balance machine, operating like an underground factory. The rotating head sits at the front of the machine, a large metal cylinder, and presses against the earth using hydraulic cylinders.
Disc cutters and scraping tools loosen the earth which is then excavated using a screw conveyor. The conveyor transports the earth on a conveyor belt through the TBM and out of the tunnel.
As the machine moves forward, it installs concrete rings to create the tunnel walls, which also provide leverage for the machine to push off. Each ring is made of seven segments, each weighing seven tonnes, and have an internal diameter of 8.10 metres.
The concrete rings being used by Anne are being manufactured by STRABAG in Hartlepool and brought to London by train, after STRABAG reopened a freight line at the Hartlepool Dock.
Two remaining TBMs, which are not yet constructed, will dig HS2’s final tunnel between Old Oak Common and Euston. Their dig will start later this year.
Image and video credit: HS2
